1. Field of the Invention
The present invention generally relates to copy protection techniques, and more particularly to methods for secure distribution of digital content.
2. Background Description
Software is big business. Software developers, including video game makers, make copies of their software and distribute these copies to purchasers using a variety of distribution channels, including retail purchase of software on compact disk (CD) media and downloading purchased software from the Internet.
A major problem for software developers is protection against unauthorized copying, and loss of revenue from sales of the software by those who make copies without permission of the developer. A variety of copy protection schemes have been developed to prevent the making of unauthorized copies. One protection scheme is to build code into the software that requires the user to provide a software key the first time the software is run or installed on the user's machine. The developer (or the developer's distributor) gives the user this key in a separate transaction at the time of purchase or at the time the software is installed. Another technique, often used where the software is distributed on CD, is to build code into the software that will prevent the software from running unless it finds an original CD in the CD drive of the computer on which the software is being run. Yet another protection scheme is to manufacture CDs in such a fashion that copies will differ from the original in certain particulars, and then build code into the software that detects these particulars as a condition to installation.
However, pirates have been successful with all these schemes in devising a way to “crack.” the copy protection mechanism and make a copy of the software that is free of copy protection and can be further copied and distributed with impunity. In each case the thief is able to obtain an original copy of the software and through various analytical techniques find a way to identify and then defeat the protection and produce copies that can be mass produced and distributed without authorization of the developer. Worse, once the protection has been defeated for one copy all other copies of the software having the same protection scheme are vulnerable. Even if expensive tools and significant effort were required to defeat the copy protection scheme, the final solution can be distributed and used with relative ease on other copies of the software.